The present invention relates to mobile radio telecommunication networks and, more particularly, management of the radio resources to be allocated to terminals in such a network.
Mobile radio telecommunication networks conventionally cover various geographical zones with the aid of various radio cells.
A terminal communicating in a radio communication network has radio resources which are allocated to it in a first cell of the network and on which it can transmit and/or receive data and/or voice. In the case where this terminal is moving, it is possible that the radio resources already allocated in this first cell may not allow this terminal to continue the communication in progress satisfactorily. In this case, new radio resources can be allocated to it in a second cell so as to allow it to communicate again under good conditions. Certain networks guarantee continuity of communication in the event of a change of cells. Such is the case with networks of cellular architecture in particular. In others, the previously established communication is broken and a new communication is established in the second cell, such is the case in certain networks of WiFi type.
Such management of radio resources comprises a step of taking a decision regarding a change of radio resources from the first cell to the second cell.
In certain telecommunication networks, such a decision to change cell is taken at the level of a centralized entity of the network which is responsible for managing a plurality of cells of the network. Such is the case in a telecommunication network based on a protocol of UMTS type (for “Universal Mobile Telecommunication System”) defined by the 3GPP standardization body (for “3rd Generation Partnership Project Agreement”). These networks are based on a hierarchized cellular architecture wherein a network entity, or base station, or else NodeB, is responsible for one or more radio cells and a central controller, or RNC (for “Radio Network Controller”), is responsible for one or more NodeB entities. In such an architecture, the radio resources allocated to a terminal in a cell associated with a NodeB, are managed by the central controller which is responsible for this NodeB.
This central controller has, in particular, information relating to the loading of the cells that it manages, as well as information relating to the signals exchanged in these cells between the NodeB entities and the terminals respectively. On the basis of this information, it is then able to take a decision to change cell for a terminal situated in one of the cells that it manages. Thus, in the event of mobility of a terminal that is currently communicating, an intercell transfer decision can be taken by the central controller. Management of the radio resources is in this case a centralized management and makes it possible to take a decision to change cells on the basis of centralized information relating to the various cells managed by the central controller.
But, in other telecommunication networks, management of the radio resources currently on the move is decentralized at the level of each cell. These networks are based on a distributed architecture, in which each cell is responsible for the cell change decisions taken in respect of its terminals.
Such is the case in the networks of WiFi type, based on the IEEE 802.11 protocol (for “Institute of Electrical and Electronics Engineer”). Thus, when a mobile terminal detects that the radio resources which are allocated to it in a cell managed by a first access point, are no longer adapted to its communication, it searches for a second access point which offers it better communication conditions. For example, the terminal determines a power level associated with a signal received from the first access point of the network which manages these communications. Next, when this power attains a relatively low level, the terminal determines power levels associated with signals received from other access points of the network. It is then able to select the second access point for the management of its communications on the basis of these various power levels. Thus, in such a context, management of the radio resources is carried out in a decentralized manner at the level of the cell and more precisely in the example described above, at the level of each of the terminals in the cell.
Generally, when the decision to change cell is taken at the cell level, whether this decision is taken at the level of the terminal itself or else at the level of the access point of the cell, it is not easy to base this decision on information relating to the radio resources in the potential target cell or cells of the change of cell.
A document WO2005084146 proposes to take into account information relating to the radio resources of the neighboring cells so as to decide a transfer of cells for a terminal of the network. More precisely, in the course of such a transfer, provision is in fact made for the base station which serves the current communication of this terminal, that is to say the server base station, to request information regarding service quality QoS (for “Quality Of Service”) from the base stations of neighboring cells. These neighboring base stations then respond to this server base station by indicating the requested QoS information. Next, this QoS information is thereafter transmitted to the terminal concerned, the latter taking the final decision regarding the cell transfer.
But, this type of radio resource management exhibits the disadvantage of generating an additional signal traffic whose quantity is directly linked with the quantity of messages exchanged in relation to the QoS information between the server base station and the various neighboring base stations.
Furthermore, the reliability of such a scheme relies on the robustness of the link between the base station of the current cell and the base stations of the potential target cells. Such a characteristic weakens the performance of this scheme under certain conditions of the network.
The present invention does not exhibit the aforesaid drawbacks.
The invention makes it possible in particular to reduce the quantity of messages requested for the consideration, at the level of a cell, of radio resource information relating to other cells of a telecommunication network.